The invention relates to a method and to apparatus for the automatic decoration of helicoid members and/or links from which to fashion articles of jewelry in precious metal, and articles of costume jewelry.
A person skilled in the art will know that in crafting chains, the option exists either of decorating a wire prior to forming the links, or of forming links which are then decorated.
Whilst the first option may turn out to be more productive in certain cases, the action of shaping the wire by bending it around a former (of quite small diameter, in some instances) occasions stretching of the molecules farthest from the former, giving rise to a so-called `orange-peel` effect.
This drawback can be avoided by adopting the second option and indeed the prior embraces machines which, utilizing appropriate tools, are designed to cart single links obtained from the turns of a helicoid wound around a rotatable former; such a former will be invested with back-and-forth movement through an axial path, and cannot be perfectly rounded.
It becomes necessary, therefore, to feed the helicoid thus formed by and between an outer support and an internal former, in such a way that the tools can grip the cut links one at a time and craft them automatically on a mass production basis, connecting them one by one to the growing chain.
The dimensions of the former must therefore remain within certain strict limits as dictated by an external support which, besides supporting the former at one end, must allow the wire, wound under tension around the former (which, not being round, does not breast completely with the wire), to run out of the other end through a fixed spiral sleeve of dimensions such as will accommodate the former together with the wire wound around it.
The helicoid wound from the wire must in fact be created by these components such that with each turn indexed, a link is fed forward to be crafted by automated steps of the process.
For the helicoid wound on the former to be fed forward successfully, the former itself must be of appropriate shape. The conventional former is substantially rectangular in profile with four corners which bite from inside the formed helicoid into the surface of the wires; the wire itself is tensioned, and the former is rotated and fed forward with the helicoid, guided by the spiral sleeve. The length of the indexing stroke is established by the pitch of the spiral sleeve.
Drawbacks are first encountered when crafting the links, which are sprung and thus tend to open cut when released and overhung so that the cutting tools may engage them. To enable these steps being carried out correctly, certain conditions must be maintained absolutely constant: the initial tension of the wire and the shape of the link (which must be looped with the butt-ends in close contact to permit of easy soldering), and the annealed state of alloyed metals making up the wire. Such requirements will always be difficult to meet, for obvious reasons. What is more, the link is invariably oval, and there is no possibility of its assuming any other shape.
A further drawback is encountered when the former has to withdraw in readiness to index through another turn and feed another link toward the cutting tools, and toward the tools which grip the links for joining purposes. It is not always the case that the former, directly engaging the wire, is successfully withdrawn so as to leave the wound helicoid perfectly motionless; what happens, conversely, is that the stretch of link springs apart when released and inhibits correct formation of the link, jeopardizing correct operation of the automatic machine.
Machines of the type in question are also beset by practical difficulties; the links turned out are invariably of an oval shape which permits of no modification whatever when adopting this particular system for formation of the helicoid.
The object of the invention is to eliminate the drawbacks thus described.